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Understanding the characteristics of the solar magnetic field is essential for interpreting solar activities and dynamo. In this research, we investigated the asymmetric distribution of the solar photospheric magnetic field values, using synoptic charts constructed from space-borne high-resolution magnetograms. It is demonstrated that the Lorentzian function describes the distribution of magnetic field values in the synoptic charts much better than the Gaussian function, and this should reflect the gradual decay process from strong to weak magnetic fields. The asymmetry values are calculated under several circumstances, and the results generally show two periodicities related to the variation of the solar B$_0$ angle and the solar cycle, respectively. We argue that it is the small-scale magnetic fields, the inclination of the solar axis, the emergence and evolution of magnetic flux, and the polar fields that are responsible for the features of asymmetry values. We further determined the polar field reversal time of solar cycles 23 and 24 with the flip of asymmetry values. Specifically, for cycle 24, we assert that the polar polarities of both hemispheres reversed at the same time - in March 2014; as to cycle 23, the reversal time of the S-hemisphere is March 2001, while the determination of the N-hemisphere is hampered by missing data., 12 pages, 8 figures; Accepted for publication in ApJ

Coronal heating is a big question for modern astronomy. Daily measurement of 985 solar spectral irradiances (SSIs) at the spectral intervals 1-39 nm and 116-2416 nm during March 1 2003 to October 28 2017 is utilized to investigate characteristics of solar rotation in the solar atmosphere by means of the Lomb \,-\, Scargle periodogram method to calculate their power spectra. The rotation period of coronal plasma is obtained to be 26.3 days, and that of the solar atmosphere at the bottom of the photosphere modulated by magnetic structures is 27.5 days. Here we report for the first time that unexpectedly the coronal atmosphere is found to rotate faster than the underlying photosphere. When time series of SSIs are divided into different cycles, and the ascending and descending periods of a solar cycle, rotation rate in the corona is also found to be larger than that in the photosphere, and this actually gives hidden evidence: it is small-scale magnetic activity that heats the corona.

The Mg II index is usually used to represent the brightening contribution to total solar irradiance (TSI) by solar bright structures, such as faculae and network. In order to understand variations of TSI, phase relations of TSI and the chromospheric Mg II index is investigated on time-scales of one year and longer. The NOAA daily Mg II index at the time interval of November 17, 1978–October 24, 2007 is utilized to carry out correlation analyses respectively with the daily ACRIM and PMOD composites of TSI. The Mg II index is found to lead TSI by about one solar rotation period for time-scales of one year and longer. Correlation of TSI with the Mg II index on the time-scale of one year is sometimes significantly positive, sometimes statistically insignificant, and sometimes even significantly negative. When sunspot darkening is dominant, the correlation between TSI and Mg II is either negative or not significant. When TSI is backward shifted vs the Mg II index by about one rotation period, correlation between them becomes significantly positive in all years. Thus, it is after about one rotation period that a more prominent intensification is inferred to be contributed to TSI than that immediately, by bright constructions, which is represented by the Mg II index. We propose an explanation for the phase relationship of TSI and the Mg II index.

In order to investigate the periodicity and long-term trends of various classes of sunspot groups (SGs), we separated SGs into two categories: simple SGs ( $A/U \leq 4.5$ , where $A$ represents the total corrected whole spot area of the group in millionths of the solar hemisphere (msh), and $U$ represents the total corrected umbral area of the group in msh); and complex SGs ( $A/U > 6.2$ ). Based on the revised version of the Greenwich Photoheliographic Results sunspot catalogue, we investigated the periodic behaviors and long-term trends of simple and complex SGs from 1875 to 1976 using the Hilbert-Huang Transform method, and we confirm that the temporal behaviors of simple and complex SGs are quite different. Our main findings are as follows. i) For simple and complex SGs, the values of the Schwabe cycle wax and wane, following the solar activity cycle. ii) There are significant phase differences (almost antiphase) between the periodicity of $53.50 \pm 3.79$ years extracted from yearly simple SG numbers and the periodicity of $56.21 \pm 2.92$ years extracted from yearly complex SG numbers. iii) The adaptive trends of yearly simple and complex SG numbers are also quite different: for simple SGs, the values of the adaptive trend gradually increase during the time period of 1875 – 1949, then they decrease gradually from 1949 to 1976, similar to the rise and the maximum phase of a sine curve; for complex SGs, the values of the adaptive trend first slowly increase and then quickly increase, similar to the minimum and rise phase of a sine curve.

Solar-cycle related variation of differential rotation is investigated through analyzing the rotation rates of magnetic fields, distributed along latitudes and varying with time at the time interval of August 1976 to April 2008. More pronounced differentiation of rotation rates is found to appear at the ascending part of a Schwabe cycle than at the descending part on an average. The coefficient $B$ in the standard form of differential rotation, which represents the latitudinal gradient of rotation, may be divided into three parts within a Schwabe cycle. Part one spans from the start to the $4^{th}$ year of a Schwabe cycle, within which the absolute $B$ is approximately a constant or slightly fluctuates. Part two spans from the $4^{th}$ to the $7^{th}$ year, within which the absolute $B$ decreases. Part three spans from the $7^{th}$ year to the end, within which the absolute $B$ increases. Strong magnetic fields repress differentiation of rotation rates, so that rotation rates show less pronounced differentiation, but weak magnetic fields seem to just reflect differentiation of rotation rates. The solar-cycle related variation of solar differential rotation is inferred to the result of both the latitudinal migration of the surface torsional pattern and the repression of strong magnetic activity to differentiation of rotation rates., 19 pages, 8 figures, accepted by MNRAS. arXiv admin note: text overlap with arXiv:1305.3970

Recently, Chandra and Vats have obtained the yearly period length of the solar coronal rotation cycle by analysing the daily adjusted solar radio flux at the 10.7-cm wavelength for the years 19472009. In this paper, we use the time series (series I) of the yearly period length to investigate the long-term variation of the rotation of radio emission corona, and we find a weak decreasing trend in the time series. We use the empirical mode decomposition to decompose both the yearly mean value (series II) of the solar radio flux at the 10.7-cm wavelength and series I into different periodical components. There is a secular trend for each of the two series, and we find a negative correlation in the two trends. The decomposed 11-yr-cycle components of the two series show different and complicated periods and there is a phase relation between them. We investigate the cycle-related variation of the coronal rotation length, and we find that there is no Schwable cycle of statistical significance for the long-term variation of the rotation cycle length.

We investigate the periodicity in the PMOD composite of the daily total solar irradiance (TSI) from 21 September 1978 to 9 June 2009. Besides the Schwabe cycle period (10.32 years), the quasi-rotation period is found to be statistically significant in TSI, whose value is about 32 days, longer than that in sunspot activity (27 days), and it intermittently appears around the sunspot maximum times. The quasi-rotation period in TSI is inferred to be mainly caused by sunspot activity, but to be modulated by bright features as well. It was previously found that variations of TSI over a Schwabe solar cycle mainly come from the combination of the sunspots’ blocking and the intensification due to bright faculae, plages, and network elements, with a slight dominance of the bright-feature effect during the maximum of the Schwabe cycle. For the sunspot-blocking and the bright-feature effect to contribute to TSI over a Schwabe solar cycle, the former is inferred to lead the latter by 29 days at least.

With the multi-waveband data, we investigated the origin and initiation of a coronal mass ejection (CME) event which happened on 23rd May 2007. This CME originated from an U-shaped filament in the active region AR10956, and the filament was not positioned strictly on the polarity inversion line of the active region. At first this filament was disturbed, then it rose slowly from the middle part. In the mean while, as shown by the extreme-ultraviolet (EUV) and soft X-ray (SXR) images, the coronal loops positioned above the filament also successively rose, and constantly expanded outward. Eventually, these coronal loops and the filament erupted altogether, along with the formation of a coronal dimming region close to the breaking position of the filament. This eruption process was accompanied with the occurrence of an X-ray class B5.3 subflare observed by the Geostationary Operational Environmental Satellite (GOES), and this subflare was related closely with the CME event in both time and space. Being consistent with the “standard” magnetic flux rope model, these solar disk activities can be regarded as the signs of the onset stage of CME on the solar disk, and the bright front of the CME probably evolved directly from the preexisted coronal loops. In addition, the relations among the event-related phenomena, such as the filament eruption, flare, the coronal loop expansion and disappearance, as well as the coronal dimming, are also discussed in this paper.

With the use of interplanetary coronal mass ejections (ICMEs) compiled by Richardson and Cane from 1996 to 2007 and the associated coronal mass ejections (CMEs) observed by the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO), we investigate the solar cycle variation of real ICME-associated CME latitudes during solar cycle 23 using Song et al.'s method. The results show the following: Although most of ICME-associated CMEs are distributed at low latitudes, there is a significant fraction of ICME-associated CMEs occurring at high latitudes. The latitudinal evolution of ICME-associated CMEs do not follow Sporer's sunspot law at low latitudes (thus, no 'butterfly diagram'); how-ever, at high latitudes, there may be a poleward motion and an equator-ward motion from the rise to the maximum to the declining phases.

The continuous complex Morlet wavelet transform is used to investigate temporal rotation cycle length of daily sunspot areas from May 9, 1874 to February 28, 2010, from a global point of view. The rotation cycle length of the Sun is found to have a secular trend: it decreased from the year of 1874 to 1950s, and since then the Sun is rotating more and more speedily in the long run. The rotation period appears around the maximum times of the Schwabe cycles with statistical significance, but in the minimum times it is always statistically insignificant, although it is found to have no relation with the Schwabe cycle. The period length of the rotation cycle displays the significant periods of 2.61 and 5.77 years.

Solar chromosphere and coronal heating is a big question for astrophysics. Daily measurement of 985 solar spectral irradiances (SSIs) at the spectral intervals 1-39 nm and 116-2416 nm during March 1 2003 to October 28 2017 is utilized to investigate phase relation respectively with daily sunspot number, the Mount Wilson Sunspot Index, and the Magnetic Plage Strength Index. All SSIs which form in the whole heated region: the upper photosphere, chromosphere, transition region, and corona are found to be significantly more correlated to weak magnetic activity than to strong magnetic activity, and to dance in step with weak magnetic activity. All SSIs which form in the low photosphere (the unheated region), which indicate the "energy" leaked from the solar subsurface are found to be more related to strong magnetic activity instead and in anti-phase with weak magnetic activity. In the upper photosphere and chromosphere, strong magnetic activity should lead SSI by about a solar rotation, also displaying that weak magnetic activity should take effect on heating there. It is thus small-scale weak magnetic activity that effectively heats the upper solar atmosphere.

The observed CME (coronal mass ejection) is its projection on the sky plane, and this leads to certain discrepancies between the observational and true parameters of the CME. For example, the observed velocity is generally smaller than the true velocity. The method of making projection correction for the CME velocity based on the conical model is utilized to analyze the velocity distributions of the 1691 CMEs which are only correlated to flares (called the class FL CMEs for short) and the 610 CMEs which are only correlated to filament eruptions (called the class FE CMEs for short) before and after the projection correction. These CMEs were observed with the Large Angle and Spectrometric Coronograph on the Solar and Heliospheric Observatory from September 1996 to September 2007 (close to a solar cycle). The obtained results are as follows: (1) before and after the projection correction the velocity distribution of FL CMEs is quite similar to that of FE CMEs, and before and after the projection correction the mean velocities of the two classes of CMEs are almost the same; (2) before and after the projection correction, the natural logarithm distribution of the FL CME velocities is also very similar to that of the FE CME velocities.

In the present study, the north-south asymmetry of filaments in solar cycles 16-21 is investigated with the use of the solar filaments observed at the Observatoire de Paris, Section de Meudon from March 1919 to December 1989. Filament activity is found regularly dominated in each of cycles 16-21 in the same hemisphere as that inferred by sunspot activity, and it is found to run in a different asymmetrical behavior at different latitudinal bands, suggesting that the north-south asymmetry of filament activity should be a function of latitudes. The regularity on the north-south asymmetry of sunspot activity given by Li et al. (2002b) is demonstrated by filament activity, The periods in the north-south asymmetry of solar filament activity are 9.13, and 12.8 years without the solar cycle found. (C) 2009 Elsevier B.V. All rights reserved.

By using the monochromatic images and magnetograms obtained with the satellite Hinode, 35 pairs of bipolar moving magnetic features (MMFs) in sunspot penumbrae are studied in the following three aspects: the morphological characteristics, velocities of motion and responses in low atmospheric layers. Then the following conclusions are drawn. (1) The bipolar MMFs appear in pairs of positive and negative polarities, are located in the midst of the approximately vertical magnetic fields in spot penumbrae, and move toward the outer boundaries of penumbrae. This indirectly justifies that the bipolar MMFs originate in the horizontal magnetic fields of penumbrae. In the time intervals of 2-8 hours and at the same positions, there appear the bipolar MMFs with similar morphologial characteristics and velocities of motion. This povides an evidence which supports the model of magnetic lines in the shape of sea serpent. (2) In the process of motion of bipolar MMFs there may appear brightenings in the photospere and chromosphere, and this implies that the middle and low layers of solar atmosphere are heated by the bipolar MMFs. (3) The sites of occurrence of bipolar MMFs and the distribution of penumbral magnetic field agree with the structural characteristics of uncombed sunspot penumbrae.

Wavelet transform methods, including the continuous wavelet transform, cross-wavelet transform and wavelet coherence, have been proposed to investigate the phase synchrony of the monthly mean flare indices in the time interval 1966 January-2007 December in the solar northern and southern hemispheres, respectively. The Schwabe cycle is the only period of statistical significance, and its mean value is 10.7 yr for the monthly mean flare indices in the northern hemisphere but slightly smaller, 10.1 yr, in the southern hemisphere - this should lead to phase asynchrony between the two. Both the cross-wavelet transform and wavelet coherence analyses show asynchronous behaviour with strong phase mixing in the high-frequency components of hemispheric flare activity, and strong synchronous behaviour with coherent phase angles in the low-frequency components, corresponding to the period-scales around the Schwabe cycle. The northern flare activity should lead the southern for the low-frequency components.

In this paper, we analyse the behaviour of the activity of coronal mass ejection (CME) observed by the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliospheric Observatory (SOHO/LASCO) in cycle 23 from 1997 to 2007 separately for the Northern and Southern hemispheres. The results show the following. (1) At all and low latitudes, the dominant hemisphere of the activity of CME changes from the Northern hemisphere before cycle maxima to the Southern hemisphere after cycle maxima; a southern dominance of the activity of CME is shown to occur in cycle 23. This is consistent with sunspot studies. The relationship between the two lines of the cumulative counts of monthly CME numbers for the Northern and Southern hemispheres is similar to those of monthly sunspot group numbers and sunspot areas. (2) At high latitudes, prior to 2002, the trend of the monthly values of the north-south asymmetry of numbers of CMEs is similar to those of sunspot group numbers and sunspot areas; the relationship between the two lines of the cumulative counts of monthly CME numbers for the Northern and Southern hemispheres is similar to those of sunspot group numbers and sunspot areas. However, after 2001, the trend of dominant hemisphere of the activity of CME at high latitudes is different from those of sunspot group numbers and sunspot areas; the relationship between the two lines of the cumulative counts of monthly CME numbers for the Northern and Southern hemispheres at high latitudes is different from those sunspot group numbers and sunspot areas. Our results seem to suggest that the activity of CME at high latitudes should have close connection with 'rush to the poles'.

We investigate the cyclic evolutionary behavior of CME accelerations for accelerating and decelerating CME events in cycle 23 from 1997 January to 2007 December. It is found that the absolute values of semiannual mean accelerations of both accelerating and decelerating CME events roughly wax and wane in a cycle, delaying the sunspot cycle in time phase. We also investigate the semiannual number of CMEs with positive and negative acceleration and find that there are more decelerating CME events than accelerating CME events during the maximum period of a cycle (about three years), but there are more accelerating CME events than decelerating CME events during the rest of the time interval of the cycle. Our results seem to suggest that the different driving mechanisms may be acting accelerate and decelerate CME events: for accelerating CME events, the propelling force (F(p)) statistically seems to play a significant role in pushing CMEs outward; for decelerating CME events, the drag (F(d)) statistically seems to play a more effective role in determining CME kinematic evolution in the outer corona. During the maximum period of a cycle, because of the V(2) dependence, F(d) is generally stronger; because of the magnetic field dependence, F(p) is also generally stronger. Thus, the absolute values of both the negative and positive accelerations are generally larger during that time. Because of the V(2) dependence, F(p) may be more effective during the maximum period of a cycle. Hence, there are more decelerating CME events than accelerating CME events during that time. During the minimum time interval of a cycle, CMEs have relatively small speeds, and F(p) may be more effective. Therefore, there are more accelerating CME events than decelerating CME events during that time.

Some historical records, which have held since the beginning of modern solar activity cycles, are being broken by the present Sun: cycle 23 records the longest cycle length and fall time; latitudes of high-latitude sunspots belonging to a new cycle around the minimum time of the cycle are statistically the lowest at present, compared with those of other cycles; there are only one or no sunspots in a month appearing at high latitudes for 58 months, which is the first time that such a long duration has been observed. The solar dynamo is believed to be slowing down due to: (1) the minimum smoothed monthly mean sunspot number is the smallest since cycle 16 onwards, and even probably among all modem solar cycles; and (2) once the time interval between the first observations of two neighboring sunspot groups is larger than 14d, it should be approximately regarded as an observation of no sunspots on the visible solar disk, called a spotless event. Spotless events occur with the highest frequency around the minimum time of cycle 24, and the longest spotless event also appears around the minimum time for observations of the Sun since cycle 16. Cycle 24 is expected to have the lowest level of sunspot activity from cycle 16 onwards and even probably for all of the modem solar cycles.

Using Howard et al.'s method, we investigate, before and after the projection correction, the speed and acceleration distributions for 1747 coronal mass ejections (CMEs) associated solely with flares (FL CMEs) and 631 CMEs associated solely with filament eruptions (FE CMEs) observed by the Large Angle and Spectrometric Coronagraph on board the Solar and Heliographic Observatory (SOHO/LASCO) from 1996 September to 2007 September, corresponding to almost an entire solar cycle. The results show the following. (1) Before the correction, the speed distributions for FL and FE CMEs are statistically different from each other; after the correction, the speed distributions for FL and FE CMEs should also be statistically different from each other. (2) Before the correction, the acceleration distributions for FL and FE CMEs are statistically different from each other. However, after the correction, FL and FE CMEs should have quite similar acceleration distributions.

Solar long-term activity runs at high latitudes in three ways: (i) in phase with solar long-term activity at low latitudes; (ii) in antiphase with solar long-term activity at low latitudes and (iii) does not follow either (i) or (ii), and mainly occurs around the times of maxima of (i) and (ii). In the present study, we investigate the north-south asymmetry of solar activity at high latitudes and found the following. In Case (i), high-latitude filament activity, for example, is inferred to have the same dominant hemisphere as low-latitude activity in a cycle. In Case (ii), the north-south asymmetry of high-latitude activity, represented by both the polar faculae and the Sun's polar field strength, is usually different from that of low-latitude activity in a sunspot cycle, and even in a cycle of high-latitude activity (polar faculae and the Sun's polar field strength), suggesting that the north-south asymmetry of solar activity at high latitudes should have little or no connection with that of low latitudes. In Case (iii), the north-south asymmetry of solar activity at high latitudes (polar flares) should have little connection with that at low latitudes as well. The observed magnetic field at high latitudes is inferred to consist of two components: one comes from the emergence of the magnetic field from the Sun's interior and the other comes from the drift of the magnetic activity at low latitudes.

Sunspot activity is usually described by either sunspot numbers or sunspot areas. The smoothed monthly mean sunspot numbers (SNs) and the smoothed monthly mean areas (SAs) in the time interval from November 1874 to September 2007 are used to analyze their phase synchronization. Both the linear method (fast Fourier transform) and some nonlinear approaches (continuous wavelet transform, cross-wavelet transform, wavelet coherence, cross-recurrence plot, and line of synchronization) are utilized to show the phase relation between the two series. There is a high level of phase synchronization between SNs and SAs, but the phase synchronization is detected only in their low-frequency components, corresponding to time scales of about 7 to 12 years. Their high-frequency components show a noisy behavior with strong phase mixing. Coherent phase variables should exist only for a frequency band with periodicities around the dominating 11-year cycle for SNs and SAs. There are some small phase differences between them. SNs lag SAs during most of the considered time interval, and they are in general more asynchronous around the minimum and maximum times of a cycle than at the ascending and descending phases.

Five solar-activity indices - the monthly-mean sunspot numbers from January 1945 to March 2008, the monthly-mean sunspot areas during the period of May 1874 to March 2008, the monthly numbers of sunspot groups from May 1874 to May 2008, the monthly-mean flare indices from January 1966 to December 2006, and the numbers of solar filaments per Carrington rotation in the time interval of solar rotations 876 to 1823 - have been used to show a systematic time delay between northern and southern hemispheric solar activities in a cycle. It is found that solar activity does not occur synchronously in the northern and southern hemispheres, and there is a systematic time lag or lead (phase shift) between northern and southern hemispheric solar activity in a cycle. About an eight-cycle period is inferred to exist in such phase shifts. The activity on the Sun may be governed by two different and coupled processes, not by a single process.

Three kinds of wavelet transform methods-continuous wavelet transform, cross-wavelet transform, and wavelet coherence-have been proposed to investigate the phase synchrony of the smoothed monthly mean sunspot areas in the time interval of 1874 May to 2008 March in the solar northern and southern hemispheres. For both time series, the Schwabe cycle is the only period of statistical significance, whose mean value is 10.61 yr. The length of the Schwabe cycle for the smoothed monthly mean sunspot areas in the northern hemisphere actually differs from that in the southern hemisphere, which should lead to phase asynchrony between the two series. Both the cross-wavelet transform and wavelet coherence analyses show an asynchronous behavior with phase mixing in the high-frequency components of hemispheric sunspot activity and a strong synchronous behavior with coherent phase angles in the low-frequency components corresponding to period scales around the Schwabe cycle. Although a phase coherence is found at timescales of about 8.5-13.5 yr (which is similar to those of Donner & Thiel, but within a shorter period), phases are not always coherent at the timescales in the considered time interval. The availability of a physical, meaningful phase definition depends crucially on the appropriate choice of reference frequencies. At the coherent period scales, the leading role is found from those conditions where processes of sunspot formation in the northern hemisphere occur earlier than in the southern one (except some exceptions in several years around the year 1900) during the years of about 1874-1926 to those where the opposite is true during the years of about 1926-1966, and returning back again during the years of about 1966-2008. The mean phase synchronization values at the coherent timescales given by wavelet coherence represent the running trend of the line of synchronization given by a cross-recurrence plot.

Sunspot activity is usually represented by either sunspot numbers (SN) or sunspot areas (SA). The smoothed monthly mean SA and SN in the northern and southern hemispheres from 1945 January to 2008 March are used to investigate the characteristics of long-term hemispheric sunspot activity. Although sunspot activity (SA and SN) is found to begin one month earlier in the northern hemisphere than in the southern hemisphere on the average of the considered time interval, the shift is so small that no long-term systematic phase shift is statistically acceptable as a first-order effect, as suggested by White & Trotter. Sunspot activity never peaks at the same time in the two hemispheres. Although the Schwabe cycle appears in hemispheric sunspot activity, its period length slightly varies during the considered time interval and seems to be longer in the southern hemisphere than in the northern hemisphere on the average. Sunspot activity is asymmetrically distributed in the hemispheres, but the largest hemispheric diversity usually does not appear around the maximum time of a cycle. The diversity of SA, respectively, in the northern and southern hemispheres runs on the Sun similarly and synchronously as the diversity of SN does. Sunspot activity is slightly asynchronous in the hemispheres.

A new index, the cumulative difference of sunspot activity in the northern and southern hemispheres, respectively, is proposed to describe the long-term behavior of the North-South asymmetry of sunspot activity and to show the balance (or bias) of sunspot activity in the two solar hemispheres on a long-term scale. Sunspot groups and sunspot areas from June 1874 to January 2007 are used to show the advantage of the index. The index clearly shows a long-term characteristic time scale of about 12 cycles in the North South asymmetry of sunspot activity. Sunspot activity is found to dominate in the southern hemisphere in cycle 23, and in cycle 24 it is predicted to dominate still in the southern hemisphere. A comparison of the new index with other similar indexes is also given.

The monthly mean numbers of polar faculae in the time interval of 1951 August to 1998 December, from observations of the National Astronomical Observatory of Japan are used to investigate the reasons which mathematically result in the asynchronization of high-latitude solar activity between the northern and southern hemispheres. It is found that the monthly mean numbers of polar faculae in the northern hemisphere three months lead those in the southern one, which should mathematically lead to phase asynchrony of the hemispheric polar-facula activity but with a slight effect. The Schwabe period length for the polar-facula activity in one hemisphere obviously differs from that in the other, which should also lead to phase asynchrony of the hemispheric polar-facula activity. It is the low-frequency components of the hemispheric polar-facula activity in period scales around the Schwabe cycle that are responsible for its strong phase synchronization. In the high-frequency components, there is a strong phase mixing, which should also lead to phase asynchrony of the hemispheric polar-facula activity.

We analyzed the speed (v) distributions of 11584 coronal mass ejections (CMEs) observed by the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliospheric Observatory (SOHO/LASCO) in cycle 23 from 1996 to 2006. We find that the speed distributions for high-latitude (HL) and low-latitude (LL) CME events are nearly identical and to a good approximation they can be fitted with a lognormal distribution. This finding implies that statistically the same driving mechanism of a nonlinear nature is acting in both HL and LL CME events, and CMEs are intrinsically associated with the source's magnetic structure on large spatial scales. Statistically, the HL CMEs are slightly slower than the LL CMEs. For HL and LL CME events respectively, the speed distributions for accelerating and decelerating events are nearly identical and also to a good approximation they can be both fitted with a lognormal distribution, thus supplementing the results obtained by Yurchyshyn et al.

The chaos of high-latitude solar activity has been investigated by determining the behavior of the monthly averaged polar facula counts obtained from the National Astronomical Observatory of Japan (NAOJ) on the basis of nonlinear dynamics theories and methods. It is found that the high-latitude solar activity is also governed by a low-dimensional chaotic attractor in both the northern and southern solar hemispheres, which is the same as that of the low-latitude solar activity. However, their maximal Lyapunov exponents are different, showing different strength of chaos. The maximal Lyapunov exponent (MLE) of polar faculae in the southern solar hemisphere is about 0.0211 +/- 0.0003 (month(-1)), which is nearly consistent with the low-latitude Wolf sunspot numbers, while the MLE in the northern one is approximately 0.0944 +/- 0.0066 (month(-1)), which is obviously greater than the above two.

Long-term variation in the distribution of the solar filaments observed at the Observatorie de Paris, Section de Meudon from March 1919 to December 1989 is presented to compare with sunspot cycle and to study the periodicity in the filament activity, namely the periods of the coronal activity with the Morlet wavelet used. It is inferred that the activity cycle of solar filaments should have them same cycle length as sunspot cycle, but the cycle behavior of solar filaments is globally similar in profile with, but different in detail from, that of sunspot cycles. The amplitude of solar magnetic activity should not keep in phase with the complexity of solar magnetic activity. The possible periods in the filament activity are about 10.44 and 19.20 years. The wavelet local power spectrum of the period 10.44 years is statistically significant during the whole consideration time. The wavelet local power spectrum of the period 19.20 years is under the 95% confidence spectrum during the whole consideration time, but over the mean red-noise spectrum of alpha = 0.72 before approximate Carrington rotation number 1500, and after that the filament activity does not statistically show the period. Wavelet reconstruction indicates that the early data of the filament archive (in and before cycle 16) are more noiseful than the later (in and after cycle 17).

For the first time, we present a rare observation of direct magnetic interaction between an erupting filament and a coronal hole (CH). The small active region filament obliquely erupted toward the CH getting in the way, met and interacted with it, and then was deflected back. The erupting filament thus underwent a distinct to-and-fro motion in the visible disk, while the CH was clearly disturbed by the interaction. Brightenings in H alpha and EUV and darkenings in He I 10830 angstrom appeared at the boundaries and in the interior of the CH. This eruption was closely associated with the initiation of a halo-type coronal mass ejection (CME). The direction of the CME, despite being greatly different from that of the initial filament eruption, was consistent with that of the reflected filament. Moreover, when the CME was seen in the limb, the filament was still in the process of the return journey in the visible disk. Therefore, it appears that the large-scale structure of the CME was bounced against and then reflected away from the CH along with the filament, and the eruptive filament represented only a very small part in the CME.

We present complementary solar observations of a filament eruption occurring in association with a halo-type coronal mass ejection ( CME) on 2006 July 6 in AR 10898. This eruption was followed by an M2.5 flare and has led to the formation of a pair of dimmings, observed in H alpha, over network patterns in regions of opposite magnetic polarities located near the ends of the eruptive filament. These dimmings, also clearly visible in He I 10830 angstrom, EUV, and soft X-rays, were preceded by distinct H alpha and EUV brightenings that first mark the dimming sites during the rise phase of the flare and then form bright edges, observable in EUV, around the growing dim regions. These dimmings have been attributed to a magnetic flux rope that is considered the origin of the CME as proposed in recent theories. The brightenings reported here are a new aspect of the CME hydromagnetic process that has not been included in existing theories. The roles and implications of the network patterns, brightenings, and sharp edges in the dimming evolutions are discussed.

We examine the nonlinear dynamical properties of the monthly smoothed group sunspot number R-g and find that the solar activity underlying the time series of R-g, is globally governed by a low-dimensional chaotic attractor. This finding is consistent with the nonlinear; study results of the monthly Wolf sunspot numbers. We estimate the maximal Lyaponuv exponent (MLE) for the R-g series to be positive and to equal approximately 0.0187 +/- 0.0023 (month(-1)). Thus, the Lyaponuv time or predictability time of the chaotic motion is obtained to be about 4.46 +/- 0.5 years, which is slightly different with the predictability time obtained from R-z. However, they both indicate that solar activity forecast should be,done only for,a short to medium term due to the intrinsic complexity of the time behavior concerned.

We analyzed multi-wavelength observations of three surges with a recurrent period of about 70 min in Ha, EUV, and soft X-ray, which occurred in the quiet-sun region on 2000 November 3. These homologous surges were associated with small flares at the same base, but their exact footpoints were spatially separated from the flare. Each surge consisted of a cool Ha component and a hot, EUV or soft X-ray component, which showed different evolutions not only in space but also in time. The EUV jets had slightly converging shapes, underwent more complicate development, showed clearly twisting structures, and appeared to open to space. The Ha surges, however, were smaller and only traced the edges of the jets. They always occurred later than the jets but had dark EUV counterparts appearing in the bright jets. These surge activities were closely associated with two emerging bipoles and their driven flux cancellations at the base region, and were consistent with the magnetic reconnection surge model. The possible cause of the delay between the surges and jets, of the dark structures in the jets are discussed, along with the possible role of flux cancellations in generation of these surges.

The interesting characteristics of long-term solar activity at high latitudes are reported as follows. (1) Two cyclic behaviours, but in anti-phase with each other, simultaneously exist at high latitudes: the magnetic fluxes in units of gauss of the line-of-sight magnetic fields at latitudes of 60 degrees-70 degrees, possibly representing the amplitude of solar magnetic activity at high latitudes, are in complete anti-phase with the solar activity at middle and low latitudes, usually represented by sunspot numbers. However, the numbers of filaments at latitudes of 60 degrees-90 degrees, possibly representing the complexity of solar magnetic activity at high latitudes, are strangely in complete anti-phase with the magnetic fluxes. (2) Two latitude migrations, but in opposite drift directions relative to each other, exist in a cycle: a poleward migration drifts from the middle latitudes toward the solar poles in the first half of a normal cycle, following an equatorward migration found from the solar poles towards the middle latitudes in the other half of the normal cycle. (3) It is inferred that polar faculae, a frequently observed phenomenon at high latitudes, are more related to the amplitude than to the complexity of solar magnetic activity at high latitudes, and they are in phase with the magnetic fluxes. (4) High-latitude flares, a violent active phenomenon at high latitudes, keep in step with neither the amplitude nor the complexity of solar magnetic activity at high latitudes; they seemingly occur just around the maximum times of both.

We report on the occurrence of Hα dimming associated with a sigmoid eruption in a quiet-sun region on 14 August 2001. The coronal sigmoid in soft X-ray images from the Yohkoh Soft X-ray Telescope was located over an Hα filament channel. Its eruption was accompanied by a flare of GOES X-ray class C2.3 and possibly associated with a halo coronal mass ejection (CME) observed with the Large Angle and Spectroscopic Coronagraphs (LASCO) on board the Solar and Heliospheric Observatory (SOHO). During the eruption, coronal bipolar double dimming took place at the regions with opposite magnetic polarities around the two sigmoid ends, but the underlying chromospheric channel did not show observable changes corresponding to the coronal eruption. Different from the erupting coronal sigmoid itself, however, the coronal dimming had a detectable chromosphere counterpart, i.e., Hα dimming. By regarding the sigmoid as a coronal sign for a flux rope, these observations are explained in the framework of the flux rope model of CMEs. The flux rope is possibly deeply rooted in the chromosphere, and the coronal and Hα dimming regions mark its evacuated feet, through which the material is possibly fed to the halo CME.

Using the data from observations of polar faculae by the National Astronomical Observatory of Japan from July 1951 to December 1998, we investigate whether there is a time lag between high-latitude solar activity and low-latitude solar activity. The cross-correlation analysis of the smoothed monthly numbers of the polar faculae with the smoothed monthly sunspot numbers shows that, high-latitude solar activity should lead low-latitude solar activity in time phase. The periodic characteristics of both of them also indicate that high-latitude activity evidently leads low-latitude activity.

A simple statistical method is used to estimate the size and timing of maximum amplitude of the next solar cycle (cycle 24). Presuming cycle 23 to be a short cycle (as is more likely), the minimum of cycle 24 should occur about December 2006 ( +/- 2 months) and the maximum, around March 2011 ( +/- 9 months), and the, amplitude is 189.9 +/- 15.5, if it is a fast riser, or about 136, if it is a slow riser. It we presume cycle 23 to be a long cycle. (as is less likely), the minimum of cycle 24 should occur about June 2008 ( +/- 2 months) and the maximum, about February 2013 ( 8 months) and the maximum will be about. 137 or 80, according as the cycle is a fast riser or a slow riser.

Three wavelet functions: the Morlet wavelet, the Paul wavelet, and the DOG wavelet have been respectively performed on both the monthly Wolf sunspot numbers (R-z) from January 1749 to May 2004 and the monthly group sunspot numbers (R-g) from June 1795 to December 1995 to study the evolution of the Gleissberg and Schwabe periods of solar activity. The main results obtained are (1) the two most obvious periods in both the R-z and R-g are the Schwabe and Gleissberg periods. The Schwabe period oscillated during the second half of the eighteenth century and was steady from the 1850s onward. No obvious drifting trend of the Schwabe period exists. (2) The Gleissberg period obviously drifts to longer periods the whole consideration time, and the drifting speed of the Gleissberg period is larger for R-z than for R-g. (3) Although the Schwabe-period values for R-z and R-g are about 10.7 years, the value for R-z seems slightly larger than that for R-g. The Schwabe period of R-z is highly significant after the 1820s, and the Schwabe period of R-g is highly significant over almost the whole consideration time except for about 20 years around the 1800s. The evolution of the Schwabe period for both R-z and R-g in time is similar to each other. (4) The Gleissberg period in R-z and R-g is highly significant during the whole consideration time, but this result is unreliable at the two ends of each of the time series of the data. The evolution of the Gleissberg period in R-z is similar to that in R-g.

In this Letter we introduce a new parameter, the sunspot unit area (SUA), which describes the daily average size of sunspots produced by the dynamo in a solar cycle. The monthly average of the SUA is studied to show its variation during the solar cycle and is compared with the two commonly used parameters, sunspot numbers and sunspot areas. Our results show that (1) the new SUA parameter waxes and wanes during sunspot cycles in the same way as the other two parameters, but with a relatively small magnitude of fluctuations, (2) the Waldmeier effect and the Gnevyshev-Ohl rule, which appear in the variations of both sunspot numbers and sunspot areas, are not shown in the variations of SUA during solar cycles, and (3) the most pronounced period of SUA variation is about 10.13 yr, which is statistically significant at any time of the considered time span.

A modified method is developed to evaluate the level of solar activity at the remainder of a progressing solar cycle based on a method previously proposed by [Li, K.J., Zhan, L.S., Wang, JX, et al., 2002a. A&A 392, 301]. The behavior of sunspot numbers at the remainder of cycle 23 is studied. A comparison of different methods that predict sunspot numbers of a whole cycle is also given in this paper. (C) 2004 Elsevier B.V. All rights reserved.

The periodicity of the high-latitude solar activity has been studied using monthly-averaged polar facula counts obtained at the National Astronomical Observatory of Japan (NAOJ) and the annual number of polar faculae observed by Mount Wilson Observatory (MWO). The complex Morlet wavelet was utilized to analyze the periodicity, in the two data sets. For the NAOJ and MWO data, the most eminent period is 10.89 and 10.48 years. respectively. which is the Schwabe period of the high-latitude solar activity. All possible periods detected at the low-latitude solar activity were also detected in the two data sets, and we found no distinct periods existing just in the two data Sets of the hi-h-latitude solar activity. The periodicity of the high-latitude solar activity is inferred to be the same as that of the low-latitude solar activity.

The paper presents the results of a study of the asymmetry of the solar active prominences (SAP) at low (less than or equal to40degrees) and high (greater than or equal to50degrees) latitudes, respectively, from 1957 through 1998 (solar cycles 19-22). A quantitative analysis of the hemispheric distribution of the SAP is given. We found that the annual hemispheric asymmetry indeed exists at low latitudes, but strangely, a similar asymmetry does not seem to occur for SAPS at high latitudes. We found that the north-south (N-S) asymmetry of the solar active prominences at high latitudes is always north dominated during solar cycles 19-22 while the N-S asymmetry of the SAPS at low latitudes is shifted to a dominance in the southern hemisphere for solar cycle 21 and remains south dominated even in cycle 22. Thus, the hemispheric asymmetry of the solar active prominences at high latitudes in a cycle appears to have little connection with the asymmetry of the solar activity at low latitudes. (C) 2003 Elsevier B.V. All rights reserved.

In the present work, the north-south asymmetry of solar activity was examined by analyzing statistically the hemispheric distribution of annual numbers of sunspot groups, using the Royal Greenwich Observatory data set from the year 1874 through 2000. An interesting phenomenon is found that the solar activity of a cycle usually has the same beginning and end times, but different maximum amplitudes at different maximum times in the hemispheres. Some characteristics of the asymmetry of solar activity were investigated and explained. For solar cycle 23, a dominance of solar activity is predicted to occur in the southern hemisphere in several forthcoming years.

In this paper, we investigate the prospect of using previously occurring sunspot cycle signatures to determine future behavior in an ongoing cycle, with specific application to cycle 23, the current sunspot cycle. We find that the gross level of solar activity (i.e., the sum of the total number of sunspots over the course of a sunspot cycle) associated with cycle 23, based on a comparison of its first several years of activity against similar periods of preceding cycles, is such that cycle 23 best compares to cycle 2. Compared to cycles 2 and 22, respectively, cycle 23 appears 1.08 times larger and 0.75 times as large. Because cycle 2 was of shorter period, we infer that cycle 23 also might be of shorter length (period less than 11 years), ending sometime in late 2006 or early 2007.

With the use of the Royal Greenwich Observatory data set of sunspot groups, an attempt is made to examine the north-south asymmetry of solar activity in the "extended" solar cycles. It is inferred that the asymmetry established for individual solar cycles does not extend to the "extended" cycles.

In the present work, the dominant hemisphere of solar activity in each of solar cycles 12 to 22 has been clarified by calculating the actual probability of the hemispheric distribution of several solar activity phenomena using long-term observational records. An attempt is made to demonstrate that a long characteristic time scale, about 12-cycle length, is inferred to occur in solar activity.

In the present study we have produced a diagram of the latitude distribution of sunspot groups from the year 1874 through 1999 and examined statistical characteristics of the mean latitude of sunspot groups. The reliability of the observed data set prior to solar cycle 19 is found quite low as compared with that of the data set observed after cycle 19. A correlation is found between maximum latitude at which first sunspot groups of a new cycle appear and the maximum solar activity of the cycle. It is inferred that solar magnetic activity during the early part of an extended solar cycle may contain some information about the strength of forthcoming solar cycle. A formula is given to describe latitude change of sunspot groups with time during an extended solar cycle. The latitude-migration velocity is found to be largest at the beginning of solar cycle and decreases with time as the cycle progresses with a mean migration velocity of about 1.61degrees per year.

In the present work, the phase relation between activities of solar active prominences respectively at low and high latitudes in the period 1957–1998 has been studied. We found that from the solar equator to the solar poles, the activity of the solar active prominences occurs earlier at higher latitudes, and that the cycle of the solar active prominences at high latitudes (larger than 50°) leads by 4 years both the sunspot cycle and the corresponding cycle of the solar active prominences at low latitudes (less than 40°).

We have collected a set of predicted values of maximum sunspot numbers of solar cycles 22 and 23 published in the literature and examined the characteristics of predictions made by various methods. The precursor methods are found to be always superior to other prediction methods. The maximum sunspot number of solar cycle 23 is here inferred to be about 162.

The D3 emission lines observed on a prominence over the solar east limb on 1984 May 5, which were found to consist of two components, i.e. the main and the broadened components, have been successfully calculated using the two-cloud model method with the multiplet of helium (3 D-3(3,2,1)-2 P-3(2,1,0)) taken into account. The results obtained show that the ejecta in front of the prominence are formed by the intermittent ejections of the matter from the plage region around the prominence, because there exist at least three distinguishable phases of the line-of-sight velocity, increasing during the observations. The turbulent velocity of the ejecta is rather large, about 29 km s(-1). The Doppler width of the ejecta is mainly the result of the non-thermal effect, and the thermal effect can be neglected compared with the non-thermal effect. The prominence is quiet and characterized by typical properties.